Hello From Kauai!

[bugwubber]

The rocket doesn't have any metal .... that metal bar was attached to the launcher

That is good news.

The statement of caution about the metal parts was "in general" since the topic came up in this thread as many people build designs from that site. At some point we should come up with a list of "recommended sites" for "how to's" with the emphasis being on being class legal and safe (meeting the competition and safety rules) so that people don't unwittingly build something unsafe or be disqualified from a record submission just because they built a design using metal parts. (this includes screws, hooks, rivets, nuts, bolts, rings, washers, fins, nozzles, tanks, couplers, tornado tubes etc.). Even the launch rail made from metal is not such a good idea as it resides next to the pressurized part of the rocket. Make sure it is securely attached to the base of the launcher so that it cannot become a projectile should your rocket explode while on the launcher. An even better solution is to utilize an internal launch tube instead.

Happy launching!

I have no concern with class recognition I am doing this for fun ... I've been launched off air craft carriers, handled in flight emergencies in the black of night over the ocean. Many of my friends are not alive today but I managed to survive. I think I can manage a rocket filled with water and air just fine

I think I read that before somewhere... ;-)
Have fun! Looking forward to see what you cook up.


Bugwubber

[Nick B]

I think you need a bigger launch gantry.

[U.S. Water Rockets]

The rocket doesn't have any metal .... that metal bar was attached to the launcher

It's always puzzled us why new people conclude that they need a massive Saturn V launch tower with gantries to launch water rockets. Anything more than an adjustable launch tube is merely overkill. We set world records with 3 pieces of scrap wood nailed together, with a launch tube fixed to it. Our advice would be to invest the time and money into the rockets and payloads. Don't get sucked into the "my launcher can beat up your launcher" wars.

That doesn't mean your launcher has to be poorly engineered or lack innovations. Our "scrap wood" launcher pioneered the Removable Launch tube and Split collar designs that are in common use today.

Do gardena rockets need a longer rail since they appear to accelerate slower?


Bugwubber

As a general rule, the answer is no. This is provided you launch vertically. If you're launching at an extreme angle with a very long rocket, it may help to have a guide. But even in that case, how much acceleration are you going to get in 5 or 6 feet of guide that is going to matter?

[U.S. Water Rockets]

The rocket doesn't have any metal .... that metal bar was attached to the launcher

It's always puzzled us why new people conclude that they need a massive Saturn V launch tower with gantries to launch water rockets. Anything more than an adjustable launch tube is merely overkill. We set world records with 3 pieces of scrap wood nailed together, with a launch tube fixed to it. Our advice would be to invest the time and money into the rockets and payloads. Don't get sucked into the "my launcher can beat up your launcher" wars.

That doesn't mean your launcher has to be poorly engineered or lack innovations. Our "scrap wood" launcher pioneered the Removable Launch tube and Split collar designs that are in common use today.

Yeah can't let the newbies get too upety and challenge ur status right?

Just trying to save you a bunch of extra work.

[air.command]

Do gardena rockets need a longer rail since they appear to accelerate slower?

Bugwubber

Hi Bugwubber,

If you are not using a launch tube that can keep the rocket upright while the rocket is on the pad you should be using a guide rail/launch tower for any rocket whether using a Gardena nozzle, pyro or otherwise. The guide rail is there for safety. Even before launch it keeps the rocket pointing up so if there is a slight breeze or the launcher moves when you are pulling the string the rocket doesn't tip over. In fact both NAR and TRA safety codes require you to use a guide rail for all rockets no matter what the size or acceleration profile is of the rocket. You would never see any club allow you to launch a rocket without a guide rail. A Gardena nozzle will not keep a rocket safely upright by itself. Any rocket you put on the pad needs to reach a stable speed by the time it leaves the launch rail. If the rocket has slower acceleration you need a longer guide rail.

- George

[Team Seneca]

The Tripoli safety code simply states that the rocket must be launched from a stable platform and must be in stable flight when it leaves the platform. The NAR safety code refers to a "rod", "tower", or "rail" you launch from to insure the rocket flies "nearly straight up". No minimum length is called out for any of these items. Since their pyro rockets cannot possibly have anything like a water rocket launch tube they don't call that out by name.

Neither code insists that the rocket has to be bound to or directed by the launcher in any way, as long as it flies along the safe flight path.

So it looks like as long as your rocket flies on a safe flight path, you can use any kind of launcher that accomplishes this.

A simple internal launch tube would be the obvious choice because it does 2 jobs: keeps the water from coming out of the rocket when the air is filled, and it accelerates the rocket before it leaves the launcher. But even that is not strictly required, provided the flight is along the safe path without it.

It's really quite simple, when you take the time to read and understand the rules.

[bugwubber]

makes sense-
Actually it just hit me what I was forgetting about- length/weight of the rocket. A tall heavy rocket would require a taller rail/tube to keep it steady regardless of acceleration.

I use a short 3" launch tube on my mini launcher and 6" tubes (above the o-ring) on the derby launcher. These have provided a good solid lock on rockets up to about 4ft long. I wouldn't try to launch an 8ft FTC noodly rocket with this setup though.

Since I'm an archery guy, I think about the release and arrow rest mechanism of a bow. The functions are almost identical. So instead of a rail or longer tube, I'm going to try an adjustable height "whisker biscuit" style guide.

Thanks,

Bugwubber

[The Mooseheads]

Bill,

It does not help having every person putting their interpretations into the discussion. Citing the different codes put forth by the pyro associations, it gets confusing. There are really several different codes that apply to rockets of all types, and those can vary from country to country. In general, the rules are very close to what is established in the United States, so I will discuss that in the most detail:

1) National Fire Protection Association (NFPA) Safety Code. NFPA code 1122 refers specifically to Model Rocketry; NFPA code 1127 covers High Power Rocketry. For information on the NFPA and to see codes 1122 and 1127 go to http://www.nfpa.org.

2) The Federal Aviation Administration (FAA) regulates air space which effects most rocketry activities. Model Rockets enjoy relief from FAA regulations via Federal Aviation Regulations Part 101; see FAR101 at http://www.access.gpo.gov

3) Tripoli Rocket Association (TRA) is a group established to promote rocketry, and they wrote own rules and regulations for competition and certification which are designed to comply with the NFPA and FAA regulations above.

4) National Association of Rocketry (NAR) is a another group established to promote rocketry, who wrote their own rules and regulations for competition and certification which are designed to comply with the NFPA and FAA regulations above.

5) Water Rocket Achievement World Record Association (WRA2) is a group established to promote a specific type of rockets (Water Rockets), who also wrote their own rules for competition, which were designed to comply with the NFPA and FAA regulations above. The NAR and Tripoli guidelines were used as a template and were modified to apply to water rockets specifically.

I want to stress that #1 and #2 on the list above supersede all of the rules below them on the list, because these are the Government Regulations that are enforced by the law. The TRA, NAR, and WRA2 rules were written to be within the confines and restrictions of the FAA and NFPA laws.

What I see here is different people mixing up and citing different rules of all of these groups, either intentionally to cause confusion or disruption, or out of ignorance or repeating bad information they received.

When you participate in a WRA2 competition launch, you MUST comply with the rules the WRA2 prescribes. just as you MUST comply with the rules set forth by the NAR and TRA at their respective launches. You CANNOT go to a NAR launch and violate their rules because you are a TRA member and the rules differ slightly. just as you CANNOT launch in a WRA2 competition and try and gain an advantage by applying the rules from NAR or TRA.

Important: If you decide to skip NAR, TRA, WRA2 membership as NickB suggested, you can do that if you understand the following:
1) Your accomplishments will not be recognized by NAR, TRA, or WRA2.
2) Your rockets MUST still comply with the FAA and NFPA regulations, otherwise you are breaking the law.

So, on this forum, when someone provides advice to someone on how to make their rocket compliant with the rules, this is not an invitation for trolls to challenge the rules which they find hard to comply with, or try and confuse the issue by citing the rules of organizations that do not conform to the WRA2 rules. This is the WRA2 forum, and we follow their rules here.

This DOES NOT preclude people from discussions about non compliant designs ON this forum. We just ask that you make it clear that you may be talking about something that is not complaint with the rules, so as not to give the impression that the non compliant topic is actually compliant. Don't be mad or surprised if another member or an administrator adds a reminder if you forget.

The WRA2 rules were established for both fairness and safety. We want to encourage people to follow them to be safe and fair and also be law abiding citizens.

One last thing: if we see people discussing topics which are clearly illegal or violations of the NFPA or FAA regulations, we insist that it be made clear that this not a legal activity, and is not recommended, condoned, or otherwise legal. In other words, don't pretend what you're doing is not against the law because you are doing it on your own and not as part of an association, or in your backyard and laws don't apply to you on your own property, and don't encourage people to copy you by showing them how to break the law or linking to external webpages or media containing instructions for lawbreaking. Such posts will be edited or deleted at the discretion of the moderators. You may also have your forum rights restricted if you do not follow these instructions.

Thanks for your attention.

edit: after writing this I realize it sounds like I am talking to Bill when I say "you" all the time, but what I meant was to address people in general on the forum. I don't want Bill to think I am saying he is doing any of these things.

[U.S. Water Rockets]

Bugwubber, The most basic texts on rocket stability show that a rocket will be unstable if the Center of Pressure is ahead of the Center of Gravity.

Consider that a typical water rocket can have several liters of water sitting at the bottom. With several kilos of water in the tail of the rocket, it is virtually impossible for the rocket to be in a stable configuration, since the center of gravity is a few cm from the rear, and the center of pressure is near the middle of the length.

This is a negatively stable condition, where any perturbation of the angle of attack will cause the rocket to completely lose stability. Which counter-intuitively explains how water rockets don't fly out of control every time. What happens is a water rocket very rapidly loses the water, which moves the center of gravity forward past the center of pressure and reaches a stable configuration. The key is that the weight leaves so rapidly, that the rocket cannot rotate about the CG before it is too late. (that's not to say you cannot force the rocket to fail to become stable by reducing the nozzle size excessively, reducing the pressure to a tiny amount, or launching it in hurricane force winds)

From this we can conclude that the typical water rocket is unstable until the water is gone. This can be 20 or 30 feet in the air for a 22mm nozzle and a small rocket, but this really isn't a problem for a water rocket because it becomes stable very rapidly.

Reducing the nozzle size by using a gardena fitting raises the altitude at which the rocket is truly stable even higher, since the water takes longer to exit. You can easily see this by watching videos on YouTube of large rockets with small nozzles. These rockets hardly ever fly straight, and often gyrate and oscillate like a drunken unicyclist. (some of this could be due to the water sloshing inside, which is another type of instability)

If one were to believe that their launch rail was somehow making their water rocket comply with some safety code that requires stability at departure, they are deluding themselves. if the code says all rockets have to be stable before losing contact with the launcher, then the rail could be 50 or 60 feet long for a small water rocket using a small nozzle. A large water rocket with a small nozzle would possibly need a rail hundreds of feet long. It is simply not possible meet this requirement with this type of rocket.

Another way to debunk the rail "requirement" is to think about it this way: Remember that the speed of the rocket does not make it more stable. The forward speed of the rocket reduces the effect of wind on the angle of attack, making it more difficult for wind to cause a deviation. If the water rocket is inherently unstable because the CG is behind the CP, it will always be unstable, no matter how fast it is flying (excluding weird effects at or near mach speed not relevant to water rockets). So, at the top of a 3 meter rail, the rocket is going faster than it was on the ground, but since it still has about 90% of the water in the bottom, it's still unstable. There is no such thing as a "stable speed" if the water is in the bottom.

Note that you could add nose weight to offset the instability caused by the water, but nobody is going to add kilograms of dry weight to a water rocket when the legal weight limit for hobby rockets is only 1500g. if your rocket weighs more than that and you have not gotten the proper clearances, you are breaking the law. The paperwork is probably not something anyone flying a water rocket will want to do.

Finally, for water rockets, there are plenty of other ways to insure that the rocket is "pointed up" and not "tipping over" that don't require rails and complex contraptions. By their nature water rockets have to have a firm connection to the air supply that pressurizes them, making the setup much more rigid and quite different than that of pyro rockets, which are typically only connected to the launch system by a piece of nichrome wire taped to the motor, necessitating the need for added mechanical devices to prevent the rocket from moving.

Try a few launches, gain some practical experience, and you will see the futility of the rail for anything other than set dressing.

[bugwubber]

....
From this we can conclude that the typical water rocket is unstable until the water is gone. This can be 20 or 30 feet in the air for a 22mm nozzle and a small rocket, but this really isn't a problem for a water rocket because it becomes stable very rapidly....

Try a few launches, gain some practical experience, and you will see the futility of the rail for anything other than set dressing.

Thanks USWR. I'm going to name my next rocket Drunken Unicyclist.

So if I read you right, stability (assuming sound design) comes from getting the water out as fast as possible?

That meshes pretty well with what I have observed.

How do you support your rockets prior to pressurization?

Here's picture that supports that idea pretty well. The water trail on the left tube was from a rocket that the kids had filled with way too much water.

DSC09925.jpg (342.97 KiB) Viewed 22 times

[Team Seneca]

I was thinking how ironic it is that anyone would insist that people use a guide rail at a association event because their rules say it must be used but they launch water rockets at those events which have several liters of water in them that push the weight well over the 1500 gram that a hobby rocket is allowed to weigh.

Where do people get the idea that they can pick and choose the rules they like from an association and follow them, and ignore the ones they don't feel like complying with?

[U.S. Water Rockets]

How do you support your rockets prior to pressurization?

Our Split Collar Cable Tie Launcher design has features to hold the rocket in place.

The launch tube inside the rocket is the same diameter as the nozzle, so the rocket will point in the same direction as the launch tube, and is supported by the tube.

The cable tie and collar arrangement grips the flange on the beck of the bottle very tightly. That allows the rocket to be held firm, regardless of the nozzle type, even if the launch tube is omitted.

The only exception to this is if you are trying to launch a very long rocket and are not pointing it vertically. A very long rocket launched at radical angles might flex while on the launcher, if only held by the very end. Very few people (if any) launch this odd configuration, so it is probably not an issue. In a situation like that there are dozens of very simple ways to support the rocket. Extending the launch tube into a tornado coupler farther up the rocket length will hold it very well. An "A" or inverted "V" made from scrap materials can be used to support such a rocket, and it simply falls away at launch.

[bugwubber]

How do you support your rockets prior to pressurization?

Our Split Collar Cable Tie Launcher design has features to hold the rocket in place.

The launch tube inside the rocket is the same diameter as the nozzle, so the rocket will point in the same direction as the launch tube, and is supported by the tube.

The cable tie and collar arrangement grips the flange on the beck of the bottle very tightly. That allows the rocket to be held firm, regardless of the nozzle type, even if the launch tube is omitted.

The only exception to this is if you are trying to launch a very long rocket and are not pointing it vertically. A very long rocket launched at radical angles might flex while on the launcher, if only held by the very end. Very few people (if any) launch this odd configuration, so it is probably not an issue. In a situation like that there are dozens of very simple ways to support the rocket. Extending the launch tube into a tornado coupler farther up the rocket length will hold it very well. An "A" or inverted "V" made from scrap materials can be used to support such a rocket, and it simply falls away at launch.

Thanks, I haven't gotten as far as pressurizing my 8ft ftc rocket. I put it on the launcher and filled it up with water so I could heat shrink a bottle end to it. It seemed kinda wet noodly. I'll do some further testing to see if a support is warranted and if so, I'm going to install something like two brooms, with the handle ends stuck in attachment points on the launcher. Maybe I can set a remote release so they fall away after I pressurize the rocket.

[U.S. Water Rockets1]

How do you support your rockets prior to pressurization?

Our Split Collar Cable Tie Launcher design has features to hold the rocket in place.

The launch tube inside the rocket is the same diameter as the nozzle, so the rocket will point in the same direction as the launch tube, and is supported by the tube.

The cable tie and collar arrangement grips the flange on the beck of the bottle very tightly. That allows the rocket to be held firm, regardless of the nozzle type, even if the launch tube is omitted.

The only exception to this is if you are trying to launch a very long rocket and are not pointing it vertically. A very long rocket launched at radical angles might flex while on the launcher, if only held by the very end. Very few people (if any) launch this odd configuration, so it is probably not an issue. In a situation like that there are dozens of very simple ways to support the rocket. Extending the launch tube into a tornado coupler farther up the rocket length will hold it very well. An "A" or inverted "V" made from scrap materials can be used to support such a rocket, and it simply falls away at launch.

Thanks, I haven't gotten as far as pressurizing my 8ft ftc rocket. I put it on the launcher and filled it up with water so I could heat shrink a bottle end to it. It seemed kinda wet noodly. I'll do some further testing to see if a support is warranted and if so, I'm going to install something like two brooms, with the handle ends stuck in attachment points on the launcher. Maybe I can set a remote release so they fall away after I pressurize the rocket.

An 8 foot FTC would be completely unstable if filled to capacity with water. The FTC is pretty strong when supporting itself, but when you fill it with water, it is very easy to kink it because it is not able to support that much weight!